After experiencing some crashes in our app, using Qt 5.15.1, I found causing component.

It is the ColorOverlay component from QtGraphicalEffects.

The ColorOverlay was created in the main window and then reparented with a bunch of other components to a different window. By reverting and repeating the process of reparenting, the app crashes at some point

After reparenting the items, there are some warning messages:

QQuickItem: Cannot use same item on different windows at the same time.

I recreated the behavior in a small test application and tried to work around the crash with a Loader. It only doesn't crash, if I connect to the windowChanged signal of the top level Item, to deactivate and activate the Loader during the reparenting process. If I only reparent the item without deactivating the Loader, the app crashes after I resize the new window.

Additionally I noticed that a component, which uses a GraphicsEffect like ColorOverlay, when loaded via a Loader it causes graphical artifacts, when the window is resized (maybe another Bug?).

Previously we used Qt 5.10.1 and the warning messages also appeared, but it didn't crashed.